System for determining final position of teeth

ABSTRACT

An apparatus and method define a fit a set of upper and lower teeth in a masticatory system of a patient by generating a computer representation of the masticatory system of the patient; and determining an occlusion from the computer representation of the masticatory system using one or more keys.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/280,509 (Attorney Docket No. 018563-005120US/9039.ALG.C2), filed Oct.25, 2002, which is a continuation of U.S. patent application Ser. No.10/047,078 (Attorney Docket No. 018563-005110/AT-00108.1), filed Jan.14, 2002, which is a continuation of application Ser. No. 09/313,291(Attorney Docket: 18563-005100/AT-00108), filed May 13, 1999 (now U.S.Pat. No. 6,406,292), which is a non-provisional of Application No.60/110,189, filed Nov. 30, 1998. The full disclosures of the aboveapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention is related generally to the field of orthodontics,and more particularly to a system and a method for graduallyrepositioning teeth.

A fundamental objective in orthodontics is to realign a patient's teethto positions where the teeth function optimally and aesthetically.Typically, appliances such as braces are applied to the teeth of thepatient by a treating orthodontist. Each appliance exerts continualforces on the teeth which gradually urge the teeth toward their idealpositions. Over a period of time, the orthodontist adjusts theappliances to move the teeth toward their final destination.

The process of attaching the braces to teeth is tedious and painful.Additionally, each visit to the orthodontist is time consuming andexpensive. The process is further complicated by uncertainties indetermining a final arrangement for each tooth. Generally, the finaltooth arrangement is determined by the treating orthodontist who writesa prescription. Traditionally, the prescription is based on theorthodontist's knowledge and expertise in selecting the intended finalposition of each tooth and without a precise calculation of forces beingexerted on the teeth when they contact each other.

BRIEF SUMMARY OF THE INVENTION

The invention provides a method for defining a fit for a set of upperand lower teeth in a masticatory system of a patient. The fit is definedby generating a computer representation of the masticatory system of thepatient and determining an occlusion from the computer representation ofthe masticatory system using one or more keys.

Implementations of the invention include one or more of the following.The key can be selected from a group consisting of a molar relationship,a crown angulation, a crown inclination, teeth rotations, teeth contactpoints, and an occlusal plane. Where the key is based on a molarrelationship, a first permanent molar may be occluded with a secondpermanent molar. Where the first permanent molar has a disto buccal cuspwith a distal surface and the second permanent molar has a mesiobuccalcusp with a mesial surface, the distal surface can occlude with themesial surface. The mesiobuccal cusp can occlude in a groove betweenmesial and middle cusps of the first permanent molar. The mesial surfacecan approach the distal surface. Moreover, the canines and premolars ofthe teeth have a cusp-embrasure relationship buccally and a cusp-fossarelationship lingually.

Where the key is based on an angulation of a crown, the method candetermine a distal inclination of a gingival portion of the crown. Thedistal inclination can be held constant for all teeth or can be constantwithin each tooth type. The angulation can be determined between afacial axis of the clinical crown (FACC) and a line perpendicular to anocclusal plane. The angulation can be minimized, positive or negative invalue.

Where the key is based on a crown inclination, the method can determinean angle formed by a line perpendicular to an occlusal plane and a linetangent to a bracket site. The crown inclination can be negative whenmeasured from an upper canine through an upper second premolar. Thecrown inclination can be progressively more negative when measured froma lower canine through a lower second molar. The crown inclination canbe between a line parallel and tangent to a facial axis of the clinicalcrown (FACC) at its midpoint and a line perpendicular to an occlusalplane.

The key can be based on tooth rotation, or on positions where the teethare free of undesirable rotations. The key can be based on a toothcontact point, where the contact point can be tight, where no spacesexist between contact points. The key can be based on an occlusal plane.The plane can range between flat to curves of Spee. The curve of Speecan be deep, slight, or reversed.

The method also includes optimizing a final placement of the teeth. Themethod can also include identifying one or more features associated withthe teeth; and generating a model of the teeth based on the identifiedfeatures. The features can be identified automatically or by a user. Thecomputer representation can be an ideal model set of teeth which can bederived from a cast of the patient's teeth or from a patient with a goodocclusion. The method also includes generating progress reportsassociated with the determined occlusion. Generated reports can bebrowsed over a network such as a wide area network (the Internet) or alocal area network. The progress report can be viewed by a patient or aclinician. The user, which can be a clinician or a patient, manipulatesthe computer representation of the masticatory system.

The method also includes generating a model the teeth; and adjustingteeth position in the model by following a prescription. The methodfurther includes generating a model of the teeth, the model having avisual appearance; and adjusting teeth position in the model until thevisual appearance of the model is satisfactory. The model can be basedon an abstract model of idealized teeth placement. The abstract modelcan be specified by one or more arch forms, or can be specified usingone or more features associated with the teeth. The teeth position canbe customized to the patient's teeth.

In another aspect, a system for generating one or more appliances for apatient includes a processor; a display device coupled to the processor;a data storage device coupled to the processor; a scanner coupled to theprocessor for providing data to model the masticatory system; means fordefining a fit between a set of upper and lower teeth in a masticatorysystem of the patient; and a dental appliance fabrication machinecoupled to the processor for generating the appliances in accordancewith the fit of the teeth.

Advantages of the invention include one or more of the following. When aprescription or other final designation is provided, a computer modelcan be generated and manipulated to match the prescription. Theprescription may be automatically interpreted in order to generate animage as well as a digital data set representing the final tootharrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational diagram showing the anatomical relationship ofthe jaws of a patient.

FIG. 2A illustrates in more detail the patient's lower jaw and providesa general indication of how teeth may be moved by the methods andapparatus of the present invention.

FIG. 2B illustrates a single tooth from FIG. 2A and defines how toothmovement distances are determined.

FIG. 2C illustrates the jaw of FIG. 2A together with an incrementalposition adjustment appliance which has been configured according to themethods and apparatus of the present invention.

FIG. 3 is a block diagram illustrating a process for producingincremental position adjustment appliances.

FIG. 4 is a flow chart illustrating a process for optimizing a finalplacement of the patient's teeth.

FIG. 5 is a flow chart illustrating a process for performing functionalocclusion on the patient's teeth.

FIG. 6 is a flow chart illustrating an optional process forincorporating midtreatment information to the final placement of thepatient's teeth.

FIG. 7 is flow chart illustrating a process for optimizing occlusionbased on one or more keys.

FIG. 8 is a flow chart illustrating a second process for performingfunctional occlusion on the patient's teeth.

FIG. 9 is a block diagram illustrating a system for generatingappliances in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a skull 10 with an upper jaw bone 22 and a lower jaw bone20. The lower jaw bone 20 hinges at a joint 30 to the skull 10. Thejoint 30 is called a temporomandibular joint (TMJ). The upper jaw bone22 is associated with an upper jaw 101, while the lower jaw bone 20 isassociated with a lower jaw 100.

A computer model of the jaws 100 and 101 is generated, and a computersimulation models interactions among the teeth on the jaws 100 and 101.The computer simulation allows the system to focus on motions involvingcontacts between teeth mounted on the jaws. The computer simulationallows the system to render realistic jaw movements which are physicallycorrect when the jaws 100 and 101 contact each other. The model of thejaw places the individual teeth in a treated position. Further, themodel can be used to simulate jaw movements including protrusivemotions, lateral motions, and “tooth guided” motions where the path ofthe lower jaw 100 is guided by teeth contacts rather than by anatomicallimits of the jaws 100 and 101. Motions are applied to one jaw, but mayalso be applied to both jaws. Based on the occlusion determination, thefinal position of the teeth can be ascertained.

Referring now to FIG. 2A, the lower jaw 100 includes a plurality ofteeth 102, for example. At least some of these teeth may be moved froman initial tooth arrangement to a final tooth arrangement. As a frame ofreference describing how a tooth may be moved, an arbitrary centerline(CL) may be drawn through the tooth 102. With reference to thiscenterline (CL), each tooth may be moved in orthogonal directionsrepresented by axes 104, 106, and 108 (where 104 is the centerline). Thecenterline may be rotated about the axis 108 (root angulation) and theaxis 104 (torque) as indicated by arrows 110 and 112, respectively.Additionally, the tooth may be rotated about the centerline, asrepresented by an arrow 114. Thus, all possible free-form motions of thetooth can be performed.

FIG. 2B shows how the magnitude of any tooth movement may be defined interms of a maximum linear translation of any point P on a tooth 102.Each point P₁ will undergo a cumulative translation as that tooth ismoved in any of the orthogonal or rotational directions defined in FIG.2A. That is, while the point will usually follow a nonlinear path, thereis a linear distance between any point in the tooth when determined atany two times during the treatment. Thus, an arbitrary point P₁ may infact undergo a true side-to-side translation as indicated by arrow d₁,while a second arbitration point P₂ may travel along an arcuate path,resulting in a final translation d₂. Many aspects of the presentinvention are defined in terms of the maximum permissible movement of apoint P₁ induced on any particular tooth. Such maximum tooth movement,in turn, is defined as the maximum linear translation of that point P₁on the tooth which undergoes the maximum movement for that tooth in anytreatment step.

FIG. 2C shows one adjustment appliance 111 which is worn by the patientin order to achieve an incremental repositioning of individual teeth inthe jaw as described generally above. The appliance is a polymeric shellhaving a teeth receiving cavity. This is described in U.S. applicationSer. No. 09/169,036, filed Oct. 8, 1998, which claims priority from U.S.application Ser. No. 08/947,080, filed Oct. 8, 1997, which in turnclaims priority from provisional application No. 06/050,352, filed Jun.20, 1997 (collectively the “prior applications”), the full disclosuresof which are incorporated by reference.

As set forth in the prior applications, each polymeric shell may beconfigured so that its tooth receiving cavity has a geometrycorresponding to an intermediate or final tooth arrangement intended forthe appliance. The patient's teeth are repositioned from their initialtooth arrangement to a final tooth arrangement by placing a series ofincremental position adjustment appliances over the patient's teeth. Theadjustment appliances are generated at the beginning of the treatment,and the patient wears each appliance until the pressure of eachappliance on the teeth can no longer be felt. At that point, the patientreplaces the current adjustment appliance with the next adjustmentappliance in the series until no more appliances remain. Conveniently,the appliances are generally not affixed to the teeth and the patientmay place and replace the appliances at any time during the procedure.The final appliance or several appliances in the series may have ageometry or geometries selected to overcorrect the tooth arrangement,i.e., have a geometry which would (if fully achieved) move individualteeth beyond the tooth arrangement which has been selected as the“final.” Such overcorrection may be desirable in order to offsetpotential relapse after the repositioning method has been terminated,i.e., to permit some movement of individual teeth back toward theirprecorrected positions. Overcorrection may also be beneficial to speedthe rate of correction, i.e., by having an appliance with a geometrythat is positioned beyond a desired intermediate or final position, theindividual teeth will be shifted toward the position at a greater rate.In such cases, the use of an appliance can be terminated before theteeth reach the positions defined by the appliance.

The polymeric shell 111 can fit over all teeth present in the upper orlower jaw. Often, only certain one(s) of the teeth will be repositionedwhile others of the teeth will provide a base or an anchor region forholding the appliance 111 in place as the appliance 111 applies aresilient repositioning force against the tooth or teeth to berepositioned. In complex cases, however, multiple teeth may berepositioned at some point during the treatment. In such cases, theteeth which are moved can also serve as a base or anchor region forholding the repositioning appliance.

The polymeric appliance 111 of FIG. 2C may be formed from a thin sheetof a suitable elastomeric polymer, such as Tru-Tain 0.03 in, thermalforming dental material, available from Tru-Tain Plastics, Rochester,Minn. Usually, no wires or other means will be provided for holding theappliance in place over the teeth. In some cases, however, it will bedesirable or necessary to provide individual anchors on teeth withcorresponding receptacles or apertures in the appliance 100 so that theappliance can apply an upward force on the tooth which would not bepossible in the absence of such an anchor.

FIG. 3 shows a process 200 for producing the incremental positionadjustment appliances for subsequent use by a patient to reposition thepatient's teeth. As a first step, an initial digital data set (IDDS)representing an initial tooth arrangement is obtained (step 202). TheIDDS may be obtained in a variety of ways. For example, the patient'steeth may be scanned or imaged using X-rays, three dimensional X-rays,computer-aided tomographic images or data sets, or magnetic resonanceimages, among others. The teeth data may be generated by a destructivescanner, as described in the incorporated-by-reference U.S. applicationSer. No. 09/169,034, filed Oct. 8, 1998.

The IDDS is then manipulated using a computer having a suitablegraphical user interface (GUI) and software appropriate for viewing andmodifying the images. More specific aspects of this process will bedescribed in detail below.

Individual tooth and other components may be segmented or isolated inthe model to permit their individual repositioning or removal from thedigital model. After segmenting or isolating the components, the userwill often reposition the tooth in the model by following a prescriptionor other written specification provided by the treating professional.Alternatively, the user may reposition one or more teeth based on avisual appearance or based on rules and algorithms programmed into thecomputer. Once the user is satisfied, the final teeth arrangement isincorporated into a final digital data set (FDDS) (step 204). The FDDSis used to generate appliances that move the teeth in a specifiedsequence. First, the centers of each tooth model may be aligned using anumber of methods. One method is a standard arch. Then, the teeth modelsare rotated until their roots are in the proper vertical position. Next,the teeth models are rotated around their vertical axis into the properorientation. The teeth models are then observed from the side, andtranslated vertically into their proper vertical position. Finally, thetwo arches are placed together, and the teeth models moved slightly toensure that the upper and lower arches properly mesh together. Themeshing of the upper and lower arches together is visualized using acollision detection process to highlight the contacting points of theteeth.

Based on both the IDDS and the FDDS, a plurality of intermediate digitaldata sets (INTDDSs) are defined to correspond to incrementally adjustedappliances (step 206). Finally, a set of incremental position adjustmentappliances are produced based on the INTDDs and the FDDS (step 208).

In step 204, final positions for the upper and lower teeth in amasticatory system of a patient are determined by generating a computerrepresentation of the masticatory system. An occlusion of the upper andlower teeth is computed from the computer representation; and afunctional occlusion is computed based on interactions in the computerrepresentation of the masticatory system. The occlusion may bedetermined by generating a set of ideal models of the teeth. Each idealmodel in the set of ideal models is an abstract model of idealized teethplacement which is customized to the patient's teeth, as discussedbelow. After applying the ideal model to the computer representation,and the position of the teeth is optimized to fit the ideal model. Theideal model may be specified by one or more arch forms, or may bespecified using various features associated with the teeth.

FIG. 4 illustrates a process 300 which optimizes the final placement ofthe teeth based on teeth features. First, the process 300 automaticallyor, with human assistance, identifies various features associated witheach tooth to arrive at a model of the teeth (step 302). An ideal modelset of teeth is then generated either from casts of the patient's teethor from patients with a good occlusion (step 303).

From step 302, the process 300 positions the model of the teeth in itsapproximate final position based on a correspondence of features to theideal model (step 304). In that step, each tooth model is moved so thatits features are aligned to the features of a corresponding tooth in theideal model. The features may be based on cusps, fossae, ridges,distance-based metrics, or shape-based metrics. Shape-based metrics maybe expressed as a function of the patient's arches, among others.

For example, cusp features associated with each tooth may be used. Cuspsare pointed projections on the chewing surface of a tooth. In adetection stage, a possible cusp is viewed as an “island” on the surfaceof the tooth, with the candidate cusp at the highest point on theisland. “Highest” is measured with respect to the coordinate system ofthe model, but could just as easily be measured with respect to thelocal coordinate system of each tooth. The set of all possible cusps isdetermined by looking for all local maxima on the tooth model that arewithin a specified distance of the top of the bounding box of the model.First, the highest point on the model is designated as the firstcandidate cusp. A plane is passed through this point, perpendicular tothe direction along which the height of a point is measured. The planeis then lowered by a small predetermined distance along the Z axis.Next, all vertices connected to the tooth and which are above the planeand on some connected component are associated with the candidate cuspas cusps. This step is also referred to as a flood fill step. From eachcandidate cusp point, outward flooding is performed, marking each vertexon the model visited in this matter as part of the correspondingcandidate cusp. After the flood fill step is complete, every vertex onthe model is examined. Any vertex that is above the plane and has notbeen visited by one of the flood fills is added to the list of candidatecusps. These steps are repeated until the plane is traveled a specifieddistance.

After the detection stage, the cusp detection process may include arejection stage where local geometries around each of the cuspcandidates are analyzed to determine if they possess non-cusp-likefeatures. Cusp candidates that exhibit non-cusp-like features areremoved from the list of cusp candidates. Various criteria may be usedto identify non-cusp-like features. According to one test, the localcurvature of the surface around the cusp candidate is used to determinewhether the candidate possesses non-cusp-like features. Alternatively, ameasure of smoothness is computed based on the average normal in an areaaround the candidate cusp. If the average normal deviates from thenormal at the cusp by more than a specified amount, the candidate cuspis rejected.

Next, the process 300 computes an orthodontic/occlusion index (step306). One index which may be used is the PAR (Peer Assessment Rating)index. In addition to PAR, other metrics such as shape-based metrics ordistance-based metrics may be used.

The PAR index identifies how far a tooth is from a good occlusion. Ascore is assigned to various occlusal traits which make up amalocclusion. The individual scores are summed to obtain an overalltotal, representing the degree a case deviates from normal alignment andocclusion. Normal occlusion and alignment is defined as all anatomicalcontact points being adjacent, with a good intercuspal mesh betweenupper and lower buccal teeth, and with nonexcessive overjet andoverbite.

In PAR, a score of zero would indicate good alignment, and higher scoreswould indicate increased levels of irregularity. The overall score isrecorded on pre- and posttreatment dental casts. The difference betweenthese scores represents the degree of improvement as a result oforthodontic intervention and active treatment. The eleven components ofthe PAR Index are: upper right segment; upper anterior segment; upperleft segment; lower right segment; lower anterior segment; lower leftsegment; right buccal occlusion; overjet; overbite; centerline; and leftbuccal occlusion. In addition to the PAR index, other indices may bebased on distances of the features on the tooth from their idealpositions or ideal shapes.

From step 306, the process 300 determines whether additionalindex-reducing movements are possible (step 308). Here, all possiblemovements are attempted, including small movements along each major axisas well as small movements with minor rotations. An index value iscomputed after each small movement and the movement with the best resultis selected. In this context, the best result is the result thatminimizes one or more metrics such as PAR-based metrics, shape-basedmetrics or distance-based metrics. The optimization may use a number oftechniques, including simulated annealing technique, hill climbingtechnique, best-first technique, Powell method, and heuristicstechnique, among others. Simulated annealing techniques may be usedwhere the index is temporarily increased so that another path in thesearch space with a lower minimum may be found. However, by startingwith the teeth in an almost ideal position, any decrease in the indexshould converge to the best result.

In step 308, if the index can be optimized by moving the tooth,incremental index-reducing movement inputs are added (step 310) and theprocess loops back to step 306 to continue computing theorthodontic/occlusion index. Alternatively, in the event that the indexcannot be optimized any more, the process 300 exits (step 312).

Turning now to FIG. 5, a process 320 for performing functional occlusionis shown. Functional occlusion is a process for determining how well theteeth fit together when the jaws move. The process 320 first acquirestooth/arch jaw registration. This may be done using conventionaltechniques such as X-ray, a computer tomography, or a mechanical devicesuch as a face bow transfer.

After acquiring the registration information, the process 320 placesdigital dental models of the teeth in a digital articulation simulator(step 324). The articulation simulator allows a subset of jaw movementssuch as bite-movements to be simulated, as described below.

From step 324, the process 320 simulates jaw motions (step 326). Asimplified set of movement physics (kinematics) is applied to the dentalmodels. The process 320 performs a simulation using a simplified set ofinteracting forces on the jaws 100 and 101 in relation to one another.The simplified physical simulation allows the system to focus on motionsinvolving much contact between the jaws. The physical simulation allowsthe system to render realistic physically correct jaw movements when thejaws 100 and 101 come into contact with each other.

A range of simulated motion may be supplied using a library of motions.One typical motion supplied by the library is a protrusive motion wherethe lower jaw 101 is moved forward and backward to bring the front teethon both jaws into contact with each other. Another motion is a lateralmotion found in food chewing. The lateral motion involves moving thejaws 100 and 101 side to side. Other motions that may be supplied in thelibrary include motions that are “tooth guided” where the path of thelower jaw 100 is guided by the teeth in contact with each other.

Next, the process 320 adjusts the final position based on contactsobserved during the simulation of motions in step 326 (step 328). Theresult of the simulation is analyzed, the position of each tooth can beadjusted if contacts associated with that tooth are deemed excessive.

Finally, based on the contact data generated, the process determineswhether additional motion simulations need to be done. The motionsimulation may be rerun until the contacts associated with each toothare acceptable to the treating orthodontist. The tooth modelmanipulation process can be done subjectively, i.e., the user may simplyreposition teeth in an aesthetically and/or therapeutically desiredmanner based on observations of the final position or based on thesimulation of contacts. Alternatively, rules and algorithms may be usedto assist the user in repositioning the teeth based on the contacts. Ifthe simulation needs to be repeated, the process loops back to step 326(step 330). Alternatively, the process exits (step 332).

FIG. 6 shows an optional process of 340 of incorporating midtreatmentinformation to the final positioning process. First, a digital modelincorporating dental information associated with the patient isgenerated from a scan of the patient's teeth (step 342). The scan may beperformed using casts, X-rays or any of the conventional scanningmethods.

Next, the digital model is segmented into one model for each tooth (step344). Each tooth is then matched against a model associated with a priorscan developed at the beginning of the treatment plan (step 346). Thematching process is based on matching corresponding points between thecurrent scan and the prior scan of the teeth. In most cases, the teethsegmented from the current scan retain the shapes determined at thebeginning of the treatment plan, and the matching process is easybecause the models should be similar to each other.

A final position transform is then applied to the new teeth model (step348). The final position and specification from the prior model iscopied to the current model of the patient, and the final position isadjusted based on the new models, the new X-ray information or a newprescription (step 350). Step 350 basically involves rerunning theminimization process 300 (FIG. 4) described previously with the newinformation, which may be a slight change in the model, a change in theX-ray scan, or a change the prescription. Finally, the process 340 exits(step 352)

FIG. 7 is a flowchart of a process 400 for determining optimal occlusionin the teeth model. The process 400 optimizes the occlusion based on sixcharacteristics (Six Keys) that were found to be consistently present ina collection of 120 casts of naturally optimal occlusion. The keysinclude a molar relationship key, a crown angulation key, a crowninclination key, teeth rotation key, teeth contact point key, and anocclusal plane key. The individual keys provide a complete set ofindicators of optimal occlusion, can be judged from tangible landmarks,and can be judged from a facial and occlusal surfaces of the crowns,thus reducing the need for a lingual view for articulating paper toconfirm occlusial interfacing. These keys are described in Lawrence F.Andrews, “The six keys to normal occlusion,” Am. J. Orthod. Vol. 62, No.3 pp. 296-309 (9/72) and in Chapter 3 of his book entitled StraightWire—The Concept and Appliance (Published by L. A. Wells), the contentsof which are incorporated by reference.

The Six Keys are interdependent elements of the structural system ofoptimal occlusion and are based on similarities in the patterns ofangulation, inclination, shape, and relative size (facial prominence) oftooth types. As such, they serve as a base for evaluating occlusion. TheSix Keys are used as treatment objectives for patients. Thecharacteristics of the Six Keys are incorporated into the design ofappliance 111 to enhance precision and consistency in treatment results.

The process 400 first checks whether optimization is to be done withrespect to a molar relationship key (step 402). If so, the process 400checks and applies an appropriate molar relationship (step 404). Themolar relationship pertains to the occlusion and the interarchrelationships of the teeth. Step 404 enforces the following sevenrequirements of the molar relationship key:

1. The mesiobuccal cusp of the permanent maxillary first molar occludesin the groove between the mesial and the middle buccal cusps of thepermanent mandibular first molar.

2. The distal marginal ridge of the maxillary first molar occludes withthe mesial marginal ridge of the mandibular second molar.

3. The mesiolingual cusp of the maxillary first molar occludes in thecentral fossa of the mandibular first molar.

4. The buccal cusps of the maxillary premolars have a cusp-embrasurerelationship with the mandibular premolars.

5. The lingual cusps of the maxillary premolars have a cusp-fossarelationship with the mandibular premolars.

6. The maxillary canine has a cusp-embrasure relationship with themandibular canine and first premolar. The tip of its cusp is slightlymesial to the embrasure.

7. The maxillary incisors overlap the mandibular incisors and themidlines of the arches match.

The cusp-groove and the marginal-ridge conditions of the molars, thecusp-embrasure relationship of the premolars and canines, and incisoroverjet can be observed directly from the buccal perspective. A facialaxis of the clinical crown (FACC) measurement is used to permitassessment of the lingual-cusp occlusion of the molars and premolarswhen these teeth are viewed from their mesiobuccal aspect, as explainedbelow.

In step 404, Interarch relationship of the posterior teeth of twodentitions can be the same, but the interfacing of the occlusal surfacesof the two dentitions may differ because of differing crowninclinations.

Step 404 ensures that correct occlusal interfacing through correctinterarch relationship, angulation, and crow inclination. Interarchrelationship and angulation are best judged from the buccal perspective;crown inclination for posterior teeth is best judged from thedentition's mesiobuccal perspective. Judging posterior occlusion firstfrom the buccal (for angulation and interarch relationship) then fromthe mesiobuccal (for inclination) provides a perspective that can besystematically described and quantified. Such information, along withother nonocclusal guidelines, are used in step 404 to identify occlusaldeviations.

Step 404 includes occluding a first permanent molar with a secondpermanent molar. In such an occlusion, the first permanent molar has adistobuccal cusp with a distal surface, the second permanent molar has amesiobuccal cusp with a mesial surface and the distal surface occludeswith the mesial surface. The mesiobuccal cusp can occlude in a groovebetween mesial and middle cusps of the first permanent molar. The mesialsurface can closely approach the distal surface. Moreover, where theteeth have canines and premolars, the canines and premolars have acusp-embrasure relationship buccally and a cusp-fossa relationshiplingually.

From step 402 to 404, the process 400 checks whether the occlusion needsto be optimized with respect to a crown angulation key (step 406). Ifso, the occlusion is optimized with respect to the crown angulation key(step 408). Essentially, step 408 ensures that all crowns should have apositive angulation, and all crowns of each tooth type should be similarin the amount of angulation. Further, the contact-area position for eachtooth type should be similar. Step 408 determines a distal inclinationof a gingival portion of the crown. The distal inclination may beconstant within each tooth type. The angulation may be determinedbetween the FACC and a line perpendicular to an occlusal plane. Step 408may minimize the angulation, which may be positive or negative.

From step 406 or step 408, the process 400 checks whether the occlusionis to be optimized with respect to a crown inclination key (step 410).If so, the crown inclination optimization is performed (step 412). Asthey do in angulation, consistent patterns also prevail in crowninclination, the following three characteristics for individual teethare analyzed in step 412.

1. Most maxillary incisors have a positive inclination; mandibularincisors have a slightly negative inclination. In most of the optimalsample, the interincisal crown angle is less than 180°. The crowns ofmaxillary incisors are more positively inclined, relative to a line 90°to the occlusal plane, than the mandibular incisors are negativelyinclined to the same line.

2. The inclinations of the maxillary incisor crowns are generallypositive—the centrals more positive than the laterals. Canines andpremolars are negative and quite similar. The inclinations of themaxillary first and second molars are also similar and negative, butslightly more negative than those of the canines and premolars. Themolars are more negative because they are measured from the grooveinstead of from the prominent facial ridge, from which the canines andpremolars are measured.

3. The inclinations of the mandibular crowns are progressively morenegative from the incisors through the second molars.

In step 412, the crown inclination can represent an angle formed by aline perpendicular to an occlusal plane and a line tangent to a bracketsite. In this step, the crown inclination can be negative when measuredfrom an upper canine through an upper second premolar. The crowninclination may become progressively more negative when measured from alower canine through a lower second molar. The crown inclination mayalso be positioned between a line parallel and tangent to the FACC atits midpoint and a line perpendicular to an occlusal plane.

From step 410 or 412, the process 400 checks whether the occlusion is tooptimized using a rotation key (step 414). If so, the process 400 checksfor undesirable rotations (step 416) and corrects the model so thattooth rotations are absent.

From step 414 or step 416, the process 400 then determines whether theocclusion needs to be optimized with respect to spacing (step 418). Ifso, the process 400 checks for tight contacts that is, no spaces shouldexist between teeth (step 420). Step 418 checks that contact points abutunless a discrepancy exists in mesiodistal crown diameter.

From step 418 or step 420, the process 400 then checks whether theocclusion is to be optimized with respect to an occlusal plane key (step422). If so, the process 400 then optimizes the teeth model by analyzingthe plane of occlusion (step 424). In step 424, the depth of the curveof Spee ranges from a flat plane to a slightly concave surface. Theplane can range between flat to curves of Spee. Moreover, the curve ofSpee may be deep, slight, or reversed. From step 422 or step 424, theprocess 400 exits.

FIG. 8 is a flow chart illustrating a second process for determiningfinal position of the patient's teeth. The process of FIG. 8 identifiesan ideal base model for the final position of the teeth that consists ofan arch curve (step 450). This model can be selected from a suite oftemplate models, derived from patients with ideal occlusion, or derivedfrom patient under treatment (via the casts, X-rays, a prescription, ordata about the patient from other sources). Next, the user of thesoftware places and orients a marker on each tooth, through which thearch curve (or curves) is intended to pass (step 452). The curves can bedesigned so that they should pass through markers placed on the tooth'sfacial, lingual, or occlusal surface. Multiple arch curves can be usedto make the specification of the final position more accurate. In step454, the position and orientation of the teeth are adjusted so that thearch curve passes through the marker on each tooth and the teeth do notoverlap. Optionally, the teeth can be made to contact each other in thisstep. Next, where the teeth have multiple markers, the position andorientation of the tooth is set so that the arch curves pass as closelyas possible through all markers on each tooth (step 456). In anotherimplementation, the markers can be automatically placed and oriented oneach tooth. The user can optionally adjust their position andorientation.

FIG. 9 is a simplified block diagram of a data processing system 500.Data processing system 500 typically includes at least one processor 502which communicates with a number of peripheral devices over bussubsystem 504. These peripheral devices typically include a storagesubsystem 506 (memory subsystem 508 and file storage subsystem 514), aset of user interface input and output devices 518, and an interface tooutside networks 516, including the public switched telephone network.This interface is shown schematically as “Modems and Network Interface”block 516, and is coupled to corresponding interface devices in otherdata processing systems over communication network interface 524. Dataprocessing system 500 may include a terminal or a low-end personalcomputer or a high-end personal computer, workstation or mainframe.

The user interface input devices typically include a keyboard and mayfurther include a pointing device and a scanner. The pointing device maybe an indirect pointing device such as a mouse, trackball, touchpad, orgraphics tablet, or a direct pointing device such as a touchscreenincorporated into the display. Other types of user interface inputdevices, such as voice recognition systems, may be used.

User interface output devices may include a printer and a displaysubsystem, which includes a display controller and a display devicecoupled to the controller. The display device may be a cathode ray tube(CRT), a flat-panel device such as a liquid crystal display (LCD), or aprojection device. The display subsystem may also provide nonvisualdisplay such as audio output.

Storage subsystem 506 maintains the basic programming and dataconstructs that provide the functionality of the present invention. Thesoftware modules discussed above are typically stored in storagesubsystem 506. Storage subsystem 506 typically comprises memorysubsystem 508 and file storage subsystem 514.

Memory subsystem 508 typically includes a number of memories including amain random access memory (RAM) 510 for storage of instructions and dataduring program execution and a read only memory (ROM) 512 in which fixedinstructions are stored. In the case of Macintosh-compatible personalcomputers the ROM would include portions of the operating system; in thecase of IBM-compatible personal computers, this would include the BIOS(basic input/output system).

File storage subsystem 514 provides persistent (nonvolatile) storage forprogram and data files, and typically includes at least one hard diskdrive and at least one floppy disk drive (with associated removablemedia). There may also be other devices such as a CD-ROM drive andoptical drives (all with their associated removable media).Additionally, the system may include drives of the type with removablemedia cartridges. The removable media cartridges may, for example behard disk cartridges, such as those marketed by Syquest and others, andflexible disk cartridges, such as those marketed by Iomega. One or moreof the drives may be located at a remote location, such as in a serveron a local area network or at a site on the Internet's World Wide Web.

In this context, the term “bus subsystem” is used generically so as toinclude any mechanism for letting the various components and subsystemscommunicate with each other as intended. With the exception of the inputdevices and the display, the other components need not be at the samephysical location. Thus, for example, portions of the file storagesystem could be connected over various local-area or wide-area networkmedia, including telephone lines. Similarly, the input devices anddisplay need not be at the same location as the processor, although itis anticipated that the present invention will most often be implementedin the context of PCS and workstations.

Bus subsystem 504 is shown schematically as a single bus, but a typicalsystem has a number of buses such as a local bus and one or moreexpansion buses (e.g., .ADB, SCSI, ISA, EISA, MCA, NuBus, or PCI), aswell as serial and parallel ports. Network connections are usuallyestablished through a device such as a network adapter on one of theseexpansion buses or a modem on a serial port. The client computer may bea desktop system or a portable system.

Scanner 520 is responsible for scanning casts of the patient's teethobtained either from the patient or from an orthodontist and providingthe scanned digital data set information to data processing system 500for further processing. In a distributed environment, scanner 520 may belocated at a remote location and communicate scanned digital data setinformation to data processing system 500 over network interface 524.

Fabrication machine 522 fabricates dental appliances based onintermediate and final data set information received from dataprocessing system 500. In a distributed environment, fabrication machine522 may be located at a remote location and receive data set informationfrom data processing system 500 over network interface 524.

Various alternatives, modifications, and equivalents may be used in lieuof the above components. Although the final position of the teeth may bedetermined using computer-aided techniques, a user may move the teethinto their final positions by independently manipulating one or moreteeth while satisfying the constraints of the prescription.

Additionally, the techniques described here may be implemented inhardware or software, or a combination of the two. The techniques may beimplemented in computer programs executing on programmable computersthat each includes a processor, a storage medium readable by theprocessor (including volatile and nonvolatile memory and/or storageelements), and suitable input and output devices. Program code isapplied to data entered using an input device to perform the functionsdescribed and to generate output information. The output information isapplied to one or more output devices.

Each program can be implemented in a high level procedural orobject-oriented programming language to operate in conjunction with acomputer system. However, the programs can be implemented in assembly ormachine language, if desired. In any case, the language may be acompiled or interpreted language.

Each such computer program can be stored on a storage medium or device(e.g., CD-ROM, hard disk or magnetic diskette) that is readable by ageneral or special purpose programmable computer for configuring andoperating the computer when the storage medium or device is read by thecomputer to perform the procedures described. The system also may beimplemented as a computer-readable storage medium, configured with acomputer program, where the storage medium so configured causes acomputer to operate in a specific and predefined manner.

Further, while the invention has been shown and described with referenceto an embodiment thereof, those skilled in the art will understand thatthe above and other changes in form and detail may be made withoutdeparting from the spirit and scope of the following claims.

1. (canceled)
 2. A computer program for use in a system for defining afit between a set of upper and lower teeth in a masticatory system of apatient and planning orthodontic treatment, the computer programresiding on a computer-readable storage medium and comprisinginstructions operable to cause a programmable processor to: determine anocclusion from a computer model of a set of upper and lower teeth of apatient's teeth; model the set of teeth in a plurality of differentarrangements representing successive repositioning of the patient'steeth from a first arrangement toward a desired arrangement; and model apatient removable appliance for each of a plurality of the arrangements,the patient removable appliances having teeth receiving cavities, thecavities of successive appliances having different geometries shaped toreceive and resiliently reposition the teeth from one arrangement towarda successive arrangement.
 3. The computer program of claim 2, whereindetermining an occlusion includes using one or more keys.
 4. Thecomputer program of claim 3, wherein one of the keys is based on a molarrelationship, a crown angulation, a crown inclination, a tooth rotation,a tooth contact point, or an occlusal plane.
 5. The computer program ofclaim 2, wherein determining an occlusion includes simulating jawmotions involving contact between a set of upper and lower teeth of apatient's teeth.
 6. The computer program of claim 5, wherein thesimulated jaw motion is supplied using a library of motions.
 7. Thecomputer program of claim 6, wherein the simulated jaw motion is aprotrusive motion, a lateral motion, or a tooth guided motion.
 8. Thecomputer program of claim 5, wherein determining an occlusion furtherincludes occluding a first permanent molar with a second permanentmolar.
 9. The computer program of claim 5, wherein the teeth includecanines and premolars and wherein the canines and premolars have acusp-embrasure relationship buccally and a cusp-fossa relationshiplingually.
 10. The computer program of claim 2, wherein determining anocclusion includes: placing a marker on a plurality of teeth of the setof teeth; and setting the position and orientation of the plurality ofteeth so that an arch curve passes through the markers within apredetermined deviation.
 11. A computer program for use in a system fordefining a fit between a set of upper and lower teeth in a masticatorysystem of a patient and planning orthodontic treatment, the computerprogram residing on a computer-readable storage medium and comprisinginstructions operable to cause a programmable processor to: determine anocclusion from a first computer representation of the masticatory systemof a patient; generate a second computer representation of themasticatory system of the patient, the generation comprising optimizingplacement of teeth by selecting occlusion index reducing movements toone or more teeth of the first computer representation; model the set ofteeth in a plurality of different arrangements representing successiverepositioning of the patient's teeth from a first arrangement toward adesired arrangement; and model a patient removable appliance for each ofa plurality of the arrangements, the patient removable appliances havingteeth receiving cavities, the cavities of successive appliances havingdifferent geometries shaped to receive and resiliently reposition theteeth from one arrangement toward a successive arrangement.
 12. Thecomputer program of claim 11, wherein the occlusion index used is a PeerAssessment Rating index.
 13. The computer program of claim 11, whereinocclusion index reducing movements are selected from attemptedmovements.
 14. A method for defining a fit between a set of upper andlower teeth in a masticatory system of a patient and planningorthodontic treatment, comprising: determining an occlusion from acomputer representation of the masticatory system; digitally modelingthe set of teeth in a first plurality of different arrangementsrepresenting successive repositioning of the patient's teeth from afirst arrangement toward a first desired arrangement; generating apatient removable appliance for each of a plurality of the arrangements;receiving a digital model of the patient's teeth comprisingmid-treatment dental information of the patient; and digitally modelinga second plurality of different arrangements of the patients based onthe mid-treatment dental information, the second plurality representingrepositioning of the patient's teeth toward a second desiredarrangement.
 15. The method of claim 14, further comprising matchingteeth of the digital model of the patient's teeth comprisingmid-treatment dental information with a previously developed digitalmodel of the patient's teeth.
 16. The method of claim 14, wherein thesecond desired arrangement is further based upon optimizing placement ofteeth by selecting occlusion index reducing movements to one or moreteeth.
 17. The method of claim 16, wherein the occlusion index used is aPeer Assessment Rating index.
 18. The method of claim 17, whereinocclusion index reducing movements are selected from attemptedmovements.